Research on areas such as collision avoidance, driving assistance, and automatic driving has been conducted in recent years, using technology for detecting objects around a vehicle with radar. For example, a radar device is provided in the front part of a vehicle and near the ground surface and detects the distance to and azimuth angle of an object. Sometimes the elevation angle of an object may also be required to be detected. Japanese Patent Application Laid-Open No. 2011-27695 discloses a radar device that can also detect the position of an object in the up-down direction. The radar device includes three element antennas arranged in the right-left direction, with the middle element antenna deviated in the up-down direction. The middle element antenna and the right-side element antenna detect the angle of an object in a first oblique direction, and the left-side element antenna and the middle element antenna detect the angle of the object in a second oblique direction. The detected two angles are used to obtain the position of the object in the up-down direction.
An on-vehicle radar device receives aground reflected wave and a direct wave by its receiving antennas, the ground reflected wave reaching the receiving antennas via a ground surface from an object, and the direct wave reaching the receiving antennas directly from the object. The radar device disclosed in Japanese Patent Application Laid-Open No. 2011-27695 detects two angles in the first and second oblique directions from a combined wave of the ground reflected wave and the direct wave and uses these angles to calculate the position of the object in the up-down direction. This requires complicated processing such as obtaining an average and variance of the positions in the up-down direction of the object that are measured for a predetermined period of time and then obtaining a corrected position of the object in the up-down direction.
The elevation angle of the object may be easily obtained by arranging a plurality of receiving antennas two-dimensionally. However, narrowing an existence range of the receiving antennas in a predetermined direction is also necessary because a vehicle has only limited available space for mounting the radar device.